This invention relates to a method and an apparatus for hydrolysis treatment of cellulosic fiber material.
In conventional systems, wood chips (or other cellulosic or fiber material) can undergo hydrolysis in a single vessel prior to treatment or cooking in a digester, such as described in U.S. Pat. Nos. 3,380,883 and 3,413,189. In such systems, hydrolysis occurs under acidic conditions in the slurry of wood chips, e.g., cellulosic material, passing through a top section of the vessel with the continued treatment of cooking in lower sections of the vessel followed by washing in the bottom of the vessel. In the upper region of the vessel, hydrolysate, e.g., C5 and C6 sugars such as pentose and hexose and other hemicellulose, is extracted from wood chips and the hydrolysate is recovered.
Hydrolysis occurs throughout the upper region of the vessel by the introduction of steam, acid and/or water in a concurrent flow in the upper region. In the lower region of the vessel, the cellulosic material is cooked and washed and is subsequently discharged as pulp from the vessel.
It is generally believed that performing the hydrolysis at a high temperature may produce the greatest volume of desired sugars. But high temperature treatment of wood or other cellulosic material may cause operational problems for the reaction vessel. For example, the treatment (hydrolysis) of cellulosic material at temperatures over 170° C. may cause the lignin to dissolve and may lead to an accumulation of the lignin in the vessel, especially on the internal surfaces. To avoid this lignin dissolving and accumulation in the vessel, the vessels may be operated at lower temperatures and for longer time. This may require a larger vessel resulting in a higher capital investment.
Other methods of hydrolyzing cellulosic material are described in U.S. application Ser. Nos. 12/114,856 (U.S. Pat. App. Pub. No. 2008/0302492) and 12/114,881 (U.S. Pat. App. Pub. No. 2008/0295981).
In certain aspects, the present invention may relate to hydrolyzing cellulosic material while minimizing any undesirable effects with respect to lignin (e.g., accumulation within the reaction vessel).